Processes for producing Friedel-Crafts reaction products and catalysts thereof are described in many literatures. For example, Hendrickson, Cram, Hammond “ORGANIC CHEMISTRY” (third edition), page 668–683(1970) describes that an aromatic compound is alkylated or acylated by the Friedel-Crafts reaction. The literature includes an example in which alkyl halide, olefin, alcohol and p-toluenesulfonylated alkane are alkylated in the presence of aluminum chloride and concentrated sulfuric acid. It also describes that an aromatic compound is acylated by aluminum chloride, boron trifluoride, hydrogen fluoride, phosphoric acid and sulfuric acid using acid halide or acid anhydride as an acylating agent. It also describes that the Fries rearrangement proceeds by aluminum chloride and the Hoesch reaction proceeds by zinc chloride as a similar example of the Friedel-Crafts reaction in view of a reaction mechanism.
The processes of synthesizing indanone, which is useful as raw materials for medicaments, include, but are not limited to, a process wherein cinnamic acid is synthesized by the Perkin reaction of benzaldehyde and the resulting cinnamic acid is reduced with hydrogen to form phenylpropionic acid, which is further converted into indanone by the intramolecular acylation reaction, and a process as shown in the following reaction scheme 1, wherein acrylic acid is reacted with thionyl chloride to form acid chloride, and the resultant acid chloride is reacted with benzene in the presence of large amounts of aluminium chloride to prepare indanone.

As shown in the following reaction scheme 2, tetralone is obtained in the similar manner. For example, benzene is reacted with succinic anhydride using an aluminum chloride reagent to form a phenylketobutyric acid, which is reduced with hydrogen to obtain phenylbutyric acid, and then tetralone is obtained by intramolecular acylation of phenylbutyric acid using an aluminum chloride reagent.

All of the processes as mentioned above require a plurality of reaction steps and are complicated. In addition, aluminium chloride, thionyl chloride, acid chloride, and the like, are fuming, errosive, and poisonous, and therefore a care must be taken in handling these substances.
C. De Castro et al., J. Molecular Catal., 134, (1998) 215–222 has reported that an indanone derivative is produced from crotonic acid and m-xylene as raw materials using a 60% phosphorus-tungsten-carrying catalyst. However, TON (the number of products per number of catalytic active sites) is very low such as 3.5 and an improvement is required in view of the synthesis.
Similarly, as the process of synthesizing an alkylcarboxylic acid containing trimethylbenzene, there is proposed a process of synthesizing the alkylcarboxylic acid by converting aldehyde of trimethylbenzene into ketocarboxylic acid by means of the Perkin reaction and reducing the resulting ketocarboxylic acid with hydrogen.
E. F. Kozhevnikova et al., Chem. Comm, 2002, (11), 1178–1179 has reported a similar reaction by means of the Fries rearrangement reaction.
As described in the prior art, zinc chloride including aluminum chloride is required as a reagent for promoting the Friedel-Crafts reaction and a polar solvent such as nitromethane or nitrobenzene is commonly used to dissolve the chloride. In addition to aluminum chloride, mineral acids such as boron trifluoride, hydrogen fluoride, phosphoric acid and sulfuric acid as well as trifluorosulfonic acid have been used.
These reagents often caused a problem in the post-treatment steps such as purification and separation after the reaction. For example, upon separation and recovering when using aluminum chloride, aluminum chloride is hydrolyzed to produce a large amount of wastes. In case of recovering the product, it is often difficult to separate the aqueous layer and the organic layer of an aluminum chloride hydrolysis solution. Because of evolution of a large amount of a hydrochloric acid gas, the material of the reactor requires acid resistance and a high-quality material must be used.
Therefore, the present invention provides a means for solving many problems described above. By providing a process for producing an aromatic compound by Friedel-Crafts reaction by reacting an aromatic compound with an ester compound in the presence of a heteropolyacid-containing solid acid catalyst, it is made possible to provide an environmentally friendly and economical process, which replaces the reaction reagent by a catalyst, thereby to prevent production of a large amount of wastes, facilitates separation and recovering of the catalyst, and sometimes enables reuse of the catalyst and eliminates the use of a reactor made of a high-quality material.
As described above, a conventional process of synthesizing indanone, tetralone and alkane having a trimethylphenyl group requires a large number of the reaction processes and was inferior in economical efficiency taking account of equipment cost, labor cost, utilities cost and waste disposal cost. The process of C. De Castro et al. is an epoch-making process for synthesizing indanone, but is insufficient in TON which exhibits catalytic performances, and the process does not describe sufficient information with respect to separation and reuse of the catalyst.